The present invention relates to a novel benzidine derivative which is suitably used as a charge transferring material, particularly hole transferring material in applications such as solar battery, electroluminescent device, electrophotosensitive material and the like, and an electrophotosensitive material using the same.
As the charge transferring material, there have been known various organic compounds such as carbazole compound, oxadiazole compound, pyrazoline compound, hydrazone compound, stilbene compound, phenylenediamine compound, benzidine compound and the like.
These charge transferring materials are normally used in a state where they are dispersed in a membrane of a suitable binding resin. In case of the electrophotosensitive material, for example, so-called organic photosensitive materials (OPC) such as single-layer type electrophotosensitive material comprising a single-layer type photosensitive layer wherein the above charge transferring material and a charge generating material which generates a charge due to light irradiation are dispersed in a binding resin, multi-layer type electrophotosensitive material comprising a charge transferring layer containing the above electric transferring material and a charge generating layer containing a charge generating material, etc. are normally used. Such an organic photosensitive material has an advantage that it is superior in processability and can be easily produced, and which offers a great degree of freedom for design of performance.
Among these compounds, there can be suitably used a 3,3'-dimethylbenzidine derivative represented by the formula: ##STR2## wherein R.sup.a, R.sup.b, R.sup.c and R.sup.d are same or different and indicate a hydrogen atom, a lower alkyl group, a lower alkoxy group or a chlorine atom, which belongs to the benzidine derivative, because of its high hole transferring capability and good compatibility with the binding resin (see Japanese Laid-Open Patent Publication No. 5-210099).
However, the above 3,3'-dimethylbenzidine derivative has such a disadvantage that it has generally low melting point (about 180.degree. C. or less) and therefore a glass transition temperature (Tg) of a membrane comprising the 3,3'-dimethylbenzidine derivative dispersed in the binding resin becomes low, which results in deterioration of durability, heat resistance and the like.
In case of the electrophotosensitive material, for example, the steps of 1 charging of the surface of the electrophotosensitive material due to corona discharge, 2 formation of a electrostatic latent image due to exposure, 3 toner development of the electrostatic latent image due to adhesion of toner, 4 image transfer of the toner image to a paper and 5 removal of the residual toner on the surface of the electrophotosensitive material after image transfer are repeated. For cleaning the residual toner, there can be used a cleaning blade which is pressure-contacted on the surface of the electrophotosensitive material. Therefore, in an electrophotosensitive material using a conventional benzidine derivative, a pressure welding dent is formed at the part where the cleaning blade has been pressure-contacted when the image forming apparatus is stopped, thereby causing various failures of image. Further, when operating the image forming apparatus, a temperature of the interior of the apparatus increases to about 50.degree. C. and therefore a recess is formed on the surface of the electrophotosensitive material, thereby causing various failures of image.